The present invention relates to a novel synthetic inorganic porous material and a method for the preparation thereof. More particularly, the invention relates to a synthetic inorganic porous material having a very large specific surface area, of which the pores have a diameter in the mesopore region with an outstandingly uniform distribution of the pore diameter as well as to a method for the preparation thereof.
Inorganic porous materials of which the pores have a diameter of 2 nm to 50 nm in the so-called mesopore region are promising as a material for which applications are now under development in the isolation or separation technology of various physiologically active substances such as vitamins and enzymes, as a catalyst in synthetic chemical processes and so on. Conventional inorganic porous materials used in these applications, such as zeolites heretofore obtained, however, have pores of which the pore diameter is about 0.9 nm at the largest. Other porous materials such as silica gel, .gamma.-alumina, active charcoal and the like have pores in the mesopore region of the pore diameter but the distribution of their pore diameter ranges so widely from 1 nm to 100 nm that they can hardly be used in a precision material-separation process or as a size-selective catalyst.
Recently, an attempt is made for the utilization of a porous material by intercalation in an application as a catalyst. An alumina-crosslinked smectite as an intercalation porous material having a specific surface area of 228 m.sup.2 /g suitable for use in the above mentioned applications is proposed in Journal of Chemical Society Communications, 1986, pages 1074-1076, according to which polyvalent cations of aluminum hydroxide are introduced between layers of smectite as an expandable layered silicate or a synthetic layer compound having a structure resembling that of smectite by cation exchange followed by a heat treatment to effect dehydration of the aluminum hydroxide forming pillars of alumina.
The porous materials obtained in this manner, however, have several problems and disadvantages. For example, the process for the synthetic preparation thereof is very complicated taking an unduly long time with poor reproducibility relative to the preparation of the aluminum hydroxide solution to be introduced between layers and the reaction of the aluminum hydroxide with smectite. The pore diameter thereof is about 0.9 nm to be close to that of faujasite zeolites so that their application fields are necessarily limited to those to which the above mentioned conventional zeolites are applicable.
Besides, the inventors have recently proposed, in Japanese Patent Kokai No. 6-48722, a porous material obtained by conducting a hydrothermal reaction of a hydrous oxide having a chemical composition of smectite and a cationic organic compound and drying and heating the thus obtained reaction product at a temperature of 100.degree. to 1000.degree. C. Though having a narrow distribution of the pore diameter in the mesopore region, this porous material is disadvantageous in respect of the large manufacturing cost because the expensive cationic organic compound combined with the hydrous oxide is necessarily lost in the course of the process by the thermal decomposition at such a high temperature.